Thyroxine (T4), Thyroxine Binding Globulin (TBG) and T4-TBG Index Blood Test
The Thyroxine (T4), Thyroxine-Binding Globulin (TBG), and T4−TBG Index Blood Test measure the TBG, T4, and T4-TBG index levels in the blood to help screen for thyroid disorders.
What is a thyroid?
The thyroid is a gland in the neck, above the collarbone, shaped like a butterfly. The thyroid is one of the endocrine glands which produce hormones. These thyroid hormones help regulate the rate of many activities in the body, such as how fast calories are burned and how fast the heart beats.
What is the purpose of this test?
Order this Thyroxine (T4), Thyroxine-Binding Globulin (TBG), and T4−TBG Index Blood Test to measure the TBG, T4, and T4-TBG index levels in the blood and help screen for thyroid disorders. TBG is a protein produced by the liver that binds to the hormones, thyroxine (T4) and triiodothyronine (T3), produced by the thyroid gland. It carries them through the bloodstream to regulate metabolism and perform other essential functions.
Thyroxine (T4) is the primary form of thyroid hormone produced by the thyroid gland. The majority of T4 is bound to proteins, while a small ratio is unbound or free. Therefore, healthcare providers sometimes evaluate the T4 and TBG levels to assess overall thyroid hormone function. This test is usually ordered for individuals showcasing thyroid disorder symptoms to help distinguish between hyperthyroidism, hypothyroidism, or other underlying health conditions.
When should I order the Thyroxine (T4), Thyroxine-Binding Globulin (TBG), and T4−TBG Index Blood Test?
Individuals may order this panel if they suspect thyroid problems. Common signs or symptoms associated with thyroid malfunction or disorders include:
- Weight loss or gain
- Painful joints and muscles
- Dry skin
- Thin/dry hair
- Irregular heart rate
- Depression and anxiety
- Mood swings
- Irregular menstrual periods
- Frequent bowel movements
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